[Bldg-sim] Residential or Nonresidental? And sizing for PTAC units.

Andrew Craig andrew_c at ieice.com
Sun Mar 9 09:51:31 PDT 2008


You are correct in treating the hotel rooms as residential spaces.  With condo projects, I have served the Appendix G model corridors or first floor offices with a HVAC system that makes more sense, such as packaged rooftop units.  There is wording in Appendix G about parts of the building that fall into other uses:

Exceptions to G3.1.1:
(a) Use additional system type(s) for non-predominant conditions
(i.e., residential/nonresidential or heating source)
if those conditions apply to more than 20,000 ft2 of conditioned
floor area.

This might not apply to your project because of the area threshold, but suggests using different HVAC systems when you have spaces of different end use.

As far as AppG PTAC efficiencies go, I would use the highest capacity in the equation and use that in the model (Resulting EER = 8.805) since you have larger loads.  In an actual project, they would just have to install multiple 1.25 ton PTACs in the room to meet the load.

Good luck,

-----Original Message-----
From: bldg-sim-bounces at lists.onebuilding.org on behalf of Loren Appin
Sent: Sun 3/9/2008 12:30 AM
To: bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] Residential or Nonresidental? And sizing for PTAC units.
Hi All,

I'm modeling a 6 story hotel, and am confused with how I should classify the
building.  The hotel is all guest rooms, and is not really mixed use.  So
according to ASHRAE this seems that it would fall under the residential
category, and I would be using PTAC or PTHP systems.  Under table G3.1.1A it
specifically says hotels are considered residential building types, not just
space types... so I assume I'm correct?   However, would I use a VAV or PSZ
system for areas that are not technically guest rooms, or does this not
matter as a hotel is considered a residential "building type"?

Also, when modeling a PTAC system it appears to me that you would get the
EER information from 6.8.1D using the equation, however, sometimes it my
system summary gives me a peak/capacity of a unit as 30KBtu or even 40 for
one room and I know that PTAC units usually don't go much about 20.  So
would the equation in this table still hold?  Finally, if I am getting
varying capacities for each unit as would be expected, would you suggest
taking an average of all the systems, and then use this capacity as the one
to enter into the equation to get the EER and then apply this EER to all
systems across the board?

Thanks so much for the help!

*Loren Appin*

Energy Engineer

*Silpa Inc.*
s i m p l e  .  s c i e n t i f i c   .   s u s t a i n a b l e


www.silpa.com | Mob: +971.50.9250895

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